At present, the clubs used by golfers at the tee, or starting area, to drive the ball over long distances are called "woods." In the beginning, these woods were manufactured in their entirety from woods such as persimmon or other similar varieties. These clubs are still prized by many golfers, but they have exhibit limited tolerance, because of the low density of the material used and its uniform distribution behind the hitting face of the club head.
To overcome this difficulty, the "metal-wood" club was devised, a club which has the shape of a wood, but whose head is made entirely of steel. Because of the high density of the material used and the weight constraints imposed, the metal-wood club normally comprises a hollow steel head generally manufactured using the lost wax casting process. In this type of construction, the weight, which is distributed mainly along the periphery of the impact face, gives a tolerance substantially greater than that of conventional woods. This tolerance also affects both the angle at which the ball leaves the club, which delineates the vertical trajectory thereof, and ball deviation, i.e., the lateral trajectory of the ball.
A first disadvantage of the metal-woods lies in the unpleasant sensations felt by the golfer at impact and resulting from the contact of metal on the ball surface.
Another disadvantage comes from the lack of optimal rigidity of the steel hitting face, whose thickness must be sufficient to withstand shock when the ball is struck. It may be demonstrated that a reduction of face rigidity increases the velocity of restoration, thereby producing a longer flight distance. It may in fact be shown that the rigidity of the face depends on the thickness of the hitting face and of the modulus of elasticity of the material used. For a given modulus of elasticity, reduction of rigidity is thus directly linked to a reduction of the thickness of this face. It has now become apparent that the optimal level of rigidity of the hitting face of a metal-wood corresponds to an excessively-small thickness, i.e., less than 3 millimeters, leading to irreversible deformation.
To solve this problem, Applicant's Patent Application No. FR 91 09001 proposes mounting a face insert made of a composite material on a hollow metal body.
Patent Application No. FR 92 02554 discloses an insert having a substantially-uniform thickness and adhesively bonded in the recess of the head body, whose support face has a geometric shape delineating horizontal and vertical curvature characteristics, i.e., bulge and roll, respectively.
U.S. Pat. No. 4,984,800 concerns a special process for manufacture of a golf club head consisting in attaching a face plate to a core by means of a number of studs fastened to the rear of the plate and cooperating with recesses formed in the core. The sub-assembly thus formed is placed in a mold, and injection is made of an epoxy resin which encloses the core and fills the space formed between the face plate and this core.
U.S. Pat. No. 3,863,932 concerns a club head having undergone sprueing and incorporating a relatively deep cavity, to the bottom of which a disk made of a dense metal is adhesively bonded. On one side, the disk is adjacent to a container containing glue and is covered with a transparent plastic material which fills the cavity. The plastic material is poured into the cavity, and all excess material is then removed by polishing, machining, or any other procedure.
Patent No. AU-A-30353/92 concerns an enlarged club head comprising a body incorporating a recess in which a face insert is mounted. The insert is attached inside the recess by means of a glue bead which fills a narrow peripheral container fitted on the edge of the recess.
In all cases, the importance of the positioning of the face insert in the recess is essential for obtaining precise, reproducible geometric characteristics of this face. However, positioning and bonding are very often neglected during head manufacture. The quantity of adhesive placed in the recess is poorly monitored and varies from one head to another. The insertion of the insert in the recess produce a fairly significant overflow of the adhesive onto the sides, and the thickness of the remaining adhesive is not uniform. Finally, the insert is more or less effectively well wedged into the recess because of the fluid nature of the adhesive. The geometrical characteristics of the head can vary tremendously from one head to another, an undesirable situation.